In the casings of turbo-engines, particularly multi-stage turbo-engines, the adapting of the thermal behavior with the passage of time to that of the rotor so as to maintain the radial gap over rotor blades and stator vanes constant upon a change in load is always a problem. It is known that, in particular, the gap around the rotor blades has a great effect on efficiency, compressor stall and fuel consumption.
In the design of this casing, the following criteria, among others, are to be taken into account, in addition to the above-mentioned behavior:
(a) low weight PA1 (b) simple manufacture=large tolerances in the case in inaccessibility/small tolerances in the case of accessibility PA1 (c) narrow receiving grooves for the feet of the stator vanes PA1 (d) easy assembly PA1 (e) easy disassembly PA1 (f) rotor bladed and screwed with (d) and (e) PA1 (g) provide grazing layers (narrow blade clearance) PA1 (h) easy repair PA1 (i) roundness of the casing during manufacture PA1 (i) continued roundness of the casing in operation PA1 (k) trueness to shape of the casing in axial direction during operation. PA1 radial stiffness and thermal inertia of the flanges PA1 simple manufacture PA1 easy assembly and disassembly of the stator vanes PA1 grazing layers in separate supports PA1 repair friendliness PA1 remaining round in operation. PA1 easy assembly and disassembly of the casing PA1 rotor bladed and screwed.
The designs known today are generally subdivided into horizontally (or vertically) divided casings and casings consisting of rings. A cup-shaped casing with suspended segments is another known possibility.
The gap control is generally effected (if provided at all) by blowing against the housing above the rotor blades.
Other problems exist in the case of horizontally or vertically divided cases.
The advantages of one construction cannot be carried over in to the other.
In the case or ring casings, the following advantages are obtained:
In the case of horizontally divided casings, the following advantages are obtained: